Tandem mass spectrometric data–FAAH inhibitory activity relationships of some carbamic acid O‐aryl esters

Abstract

We have recently described a class of systemically active inhibitors of the intracellular activity of fatty acid amide hydrolase (FAAH) and traced extensive structure-activity relationships. These compounds, characterized by an N-alkyl carbamic acid O-aryl ester structure, exert potent anxiolytic-like effects in animal models. In the present study, possible relationships between mass spectrometric parameters (related to the propensity of the C(O) -O bond to be cleaved) and FAAH-inhibitory potency were tested. With this aim, a set of our products was analyzed by electrospray ionization mass spectrometry and the protonated molecules were decomposed by low-energy collisions. The experiments were performed by ion trap mass spectrometry, which led to a step-by-step energy deposition, thus favouring the lowest critical energy decomposition channels.

Correlation between energetics of collisionally activated decompositions, interaction energy and biological potency of carbamate FAAH inhibitors

“…5 This supported the hypothesis that the ease of C(O)-O bond cleavage was relevant to explain FAAH inhibition. The results thus obtained justified the proposal of a binding mode to FAAH, 5,8,9 later supported by other authors, 13 alternative to that initially hypothesized.…”

“…5 This supported the hypothesis that the ease of C(O)-O bond cleavage was relevant to explain FAAH inhibition. The results thus obtained justified the proposal of a binding mode to FAAH, 5,8,9 later supported by other authors, 13 alternative to that initially hypothesized. 7 In the present investigation we applied the previously described approach to a series of biphenyl-3-yl carbamate analogs of URB524 (19, Table 1) with electron-withdrawing or electron-donating substituents on the distal (1-10, Table 1) 8 and proximal (11-18, Table 1) 9 phenyl rings.…”

“…1 Quite early we used MS techniques to establish quantitative SARs for some potential anticancer agents (aryl and heteroaryl triazenes), 2 -4 and more recently for novel inhibitors of the fatty acid amide hydrolase (FAAH) enzyme. 5 The latter compounds are characterized by an N-alkylcarbamic acid O-aryl ester structure, and they can be exemplified by the irreversible and systemically active inhibitor cyclohexylcarbamic acid 3 0 -carbamoylbiphenyl-3-yl ester (URB597). 6 The chemical rationalization of the mode of action of these FAAH inhibitors and their SARs were approached by modeling studies 7 -9 and also by MS techniques.…”

“…In this particular case, the second step was studied by breakdown curves, 12 relative to ESI-generated protonated molecules, which, taking place under collisional conditions during resonance excitation in an ion trap, exclusively gave fragments related to the C(O)-O bond cleavage. 5 The crossing points (CPs) (corresponding to the collision energy necessary to fragment 50% of the precursor ion population) between the decreasing [MH] C ion abundance and the increasing ion fragment abundance w (Scheme 2) were related to the energetics Ł Correspondence to: P. Traldi, CNR-ISTM, Corso Stati Uniti 4, …”

Understanding the role of carbamate reactivity in fatty acid amide hydrolase inhibition by QM/MM mechanistic modelling

“…1), can be docked in two possible orientations (called orientations I and II) within the FAAH catalytic site. 6,7 Recently, hybrid quantum mechanical/molecular mechanics (QM/MM) modelling, 8 using the B3LYP/6-31G(d)//PM3-CHARMM22 potential, showed that the inhibitory process is energetically preferred in orientation II. 9 This orientation allows the catalytic nucleophile, Ser241, to efficiently attack the carbonyl group of URB524 (Fig.…”